GFRP增强方钢管再生块体混凝土柱的受剪性能试验研究

Shear tests on square steel tubular columns incorporating DCLs and wrapped with GFRP sheets

对再生块体混凝土构件施加外部约束是提高其受力性能的有效途径,通过13根方钢管再生块体混凝土柱试件与10根GFRP增强方钢管再生块体混凝土柱试件的受剪性能试验,考察了废旧混凝土块体取代率、剪跨比、轴压比及环向GFRP层数等参数对试件横向剪力-变形曲线与受剪承载力的影响,检验了采用现有设计公式预测试件受剪承载力的有效性。研究表明:方钢管再生块体混凝土柱及GFRP增强方钢管再生块体混凝土柱的受剪性能受剪跨比和轴压比的影响较大,其横向剪力-变形曲线随上述两参数变化呈现3种典型形态;当废旧混凝土块体取代率低于35%且新、旧混凝土强度差不超过15 MPa时,再生块体对柱受剪性能的影响总体较小;剪跨比不大于0.5时环向粘贴单层GFRP布对柱受剪承载力的提升无明显效果,而双层GFRP布可小幅提高柱的受剪承载力;相比现有钢管混凝土柱受剪承载力计算公式,所提计算式可较好地预测方钢管及GFRP增强方钢管再生块体混凝土柱的受剪承载力。

It is effective to improve the mechanical performance of structural members made with recycled lump concrete by providing external confinement. A total of 23 square steel tubular columns filled with demolished concrete lumps(DCLs) and fresh concrete(FC) were tested in shear, out of which 10 columns were wrapped with glass fiber-reinforced polymer(GFRP) sheets and 13 were without the wrapping. The effects of replacement ratio of DCLs, shear span-to-depth ratio, axial load ratio, and number of layers of GFRP sheet(applied in hoop direction) on shear force-deforma-tion curves and shear capacity of specimens were investigated. Moreover, the effectiveness of existing shear design formulas was examined by comparing the predictions from those formulas with the experimentally obtained results. From this study, it can be concluded that both the shear span-to-depth ratio and the axial load ratio have a substantial effect on the shear performance of the tested specimens, leading to three different shapes of shear response curves;the effect of the replacement ratio is overall limited when it is less than 35% and the strength difference between new and old concrete is no greater than 15 MPa;at a small shear span-to-depth ratio(λ≤ 0.5), one-ply GFRP wrapping has little effect on enhancing the specimens’ shear capacity, but in the case of two-ply wrapping, a small gain in strength is observed;compared with the current shear design formulas specific to conventional concrete-filled steel tubular columns, the design formula proposed in this paper is able to accurately predict the shear capacity of the square steel tubular columns incorporating DCLs and wrapped with/without GFRP sheets.